1. Field of the Invention
The present invention relates to a nonaqueous electrolyte battery.
2. Description of the Related Art
A nonaqueous electrolyte battery in which the charging and discharging operations are performed through migration of lithium ions between the negative electrode and the positive electrode, is currently researched and developed as a high energy density battery. It is desired that the negative electrode active material for the nonaqueous electrolyte battery has a high capacity and a long life.
At present, it is a common practice that a carbonaceous material is used for the negative electrode active material. The carbonaceous material has a long life, but a little lithium storage amount, and a capacity of the material are small. To cope with this problem, there is an approach to use alloys or the like for the high-capacity negative electrode active material. However, the volume expansion of the alloy is remarkably large and the life thereof is short because the lithium storing and releasing reaction of the alloy is performed through the alloying reaction.
The inventors of the present patent application disclosed an intermetallic compound having an La3Co2Sn7 crystal structure as a negative electrode active material with a high capacity and long life in an article by Shinsuke Matsuno, Tatsuoki Kohno, Norio Takami, Fumiyuki Kawashima, and Takao Sawa, “La3Co2Sn7 Ternary Intermetallic Phase for Lithium Insertion and Deinsertion”, Electro Chemical and Solid-State Letters, Mar. 1, 2005, 8(4)A234-A236”. A capacity of the intermetallic compound per unit volume is two to three times as large as that of the carbonaceous material. The lithium storing/releasing reaction of the intermetallic compound is performed through the reversible lithium insertion reaction. For this reason, a long life of battery is realized by using the intermetallic compound.